1. Field of the Invention
The present invention relates to a coating liquid application apparatus that applies to a printed surface of a print medium a coating liquid or the like for improving weatherability and glossiness of the printed surface, an image printing apparatus having the liquid application apparatus, and a coating liquid application method.
2. Description of the Related Art
Image printing apparatus with functions of printers, copying machines and facsimiles or image printing apparatus used as output devices for composite machines and workstations, including computers and word processors, are constructed to print images (including characters and symbols) on print mediums such as paper and plastic thin sheet (e.g., OHP) according to image information. The image printing apparatus may be classified into an ink jet printing system, a wire dot printing system, a thermal printing system, a thermal transfer printing system, and a laser beam printing system according to the printing method of the printing means used.
Of these, the ink jet system has been spotlighted in recent years as a printing system that can easily produce an image quality almost identical with that of a silver salt picture. An ink jet system using a dye ink in particular has an excellent color reproducibility and can produce a high image quality equal to or even higher than that of a silver salt picture system. The ink jet printing system, however, has a problem that an output printed medium has poor weatherability and is known to fade when subjected to gases such as ozone, light and water. Hence, it has conventionally been proposed to laminate the printed medium, on which an image was formed, with a film or the like to prevent a possible degradation of the printed image.
Other conventional methods that have been proposed or practiced to deal with this problem include using special glossy paper, increasing the amount of ink to be ejected, or laminating the printed surface as described above.
It is, however, considered difficult to construct a post processing device, that performs the laminate processing as described above, in such a way that the user can easily handle it. To realize the post processing device which can automatically laminate the print medium, there are the following problems that need to be solved.
First, there is a problem of running cost. The laminate processing generally involves bonding to the print medium under pressure or by heat a transparent film, larger in size than the print medium, which is coated with an adhesive. Hence, when the size changes, excess portions must be removed, increasing the running cost.
A second problem is an increased size of the post processing device and its installation space. In performing the laminate processing, the post processing device needs a space therein in which to form a laminate film in advance in conformity with the shape of a cartridge accommodating the laminate film for easy replacement of the film or in which to cut the laminated print medium, and also a space in which to accommodate an excess laminate material. This in turn increases the size of the post processing device and requires a large space for its installation.
A third problem is device cost. To automatically laminate a print medium in a required size, which was inserted by the user or automatically printed with an image by the printing apparatus, ancillary portions such as a film storage portion and a print medium cutting mechanism are required in addition to the laminate processing mechanism, increasing the overall cost of the apparatus.
To eliminate these problems, it is conceivable that the ancillary portions such as the cutting mechanism may be omitted and that the excess part that was formed after the laminate processing may be cut off by the user. However, this will drastically increase the work that needs to be done by the user, significantly deteriorating the performance of the post processing device.
While a process is proposed which transfers only the laminate layer as by heat (so-called thermal transfer process), the use of the laminate layer that can easily be transferred requires the film strength to be reduced. This gives rise to new problems, such as the overall print medium becoming very weak in terms of mechanical strength and a base material for holding the laminate layer becoming waste after the process.
Further, the thermal ink jet printing system using electrothermal transducers heats ink to project an ink droplet, so that there is a limitation on the kind of ink that can be used. For example, the use of an ink with a sufficiently high dye density raises problems that need to be solved to prevent a scorching of the ink. Therefore, it is difficult to improve the density of an image using such an ink.
Further, when a print medium that has undergone preprocessing for enhancing the image density, such as glossy paper, is used as described earlier, the print medium itself becomes very expensive, increasing the running cost. Further, when the amount of ink to be ejected is increased, problems such as the spreading of printed ink and the waving of the print medium become more likely to occur, depending on the amount of ink that the print medium can absorb.